1. Field of the Invention
This disclosure relates to the field of x-ray imaging, and more particularly to the dynamic low-dose imaging of an object or subject with a moving detector, as well as to the dynamic low-dose tomosynthesis and limited-angle tomographic imaging of a subject with a moving detector and a moving x-ray source. Specific applications are in the sub-fields of fluoroscopy, radiography, and cardiology. Other applications are in the fields of non-destructive testing, homeland security, and animal imaging.
2. Description of the Related Art
A number of interventional procedures utilize x-ray as the preferred imaging modality for intervention planning, guidance, monitoring, and control. Although x-ray imaging systems for this purpose are widely available, prior-art systems and approaches are significantly limited. In particular, prior art interventional imaging poses the major impediments of high subject radiation dose and cumulative physician exposure to radiation. In certain procedures, the subject x-ray dose may be high enough to bum the subject's skin. Furthermore, a significant fraction of experienced radiologists and cardiologists are approaching or have reached their annual or life-time accumulated dose limit, and are therefore prevented from, or limited in, the practice of their skills.
In a typical fluoroscopic procedure, an area detector is used to provide a fairly wide imaging field (typically 6 to 16 inches) at a high refresh rate (30 frames per second, or higher). Over the years, image-intensifier technology has evolved to provide electronic amplification and viewing of images. In general, the x-ray image formed on an input phosphor screen is amplified in intensity by a very large factor, by the electronics of a vacuum envelope within an image intensifier. The bright, but typically reduced-area output image is electronically recorded by a video system, and then displayed to the physician in essentially real time. Recently, a number of vendors have introduced digital detectors with refresh rate and x-ray absorption efficiency comparable to that of the image intensifier. However, these improvements have not resolved the issues of high subject and attendant dosage.
Current technologies are further limited, in part, due to use of large area detectors and large exposure area beams. While a number of systems currently offered provide adjustable field-of-view imaging, a large exposure field is desirable to allow the physician to track the progress of an intervention and to maintain view of specific anatomical landmarks during a procedure. The requirement for a large exposed area translates into high detector costs and the need for a scatter-rejecting Bucky grid, which absorbs about one-half of emitted radiation and thus requires that the applied dose be increased by a factor of two. This adds to the aforementioned high subject and attendant dose; furthermore, the requirement for a large exposed area results in relatively low refresh rates over the entire image. For example, read-out of an entire large area detector, or a large area of such a detector, limits the imaging refresh rate.
Cardiology and neurology interventions, which typically require the insertion of a catheter or similar interventional device in the subject's vasculature, can necessitate continuous or intermittent subject exposures for extended durations, resulting in high x-ray doses. For example, specific cardiology procedures using current, known technologies, such as in electro-physiology, can last for more than one hour, and accordingly necessitate very high subject doses. Interventional radiologists, cardiologists and other attending staff are also subject to significant x-ray exposure and dose, to such a degree that dose limitation regulations may prevent them from active work for a significant fraction of their available time, thus leading to underutilization of expensive resources.
Three-dimensional (3D) imaging currently requires complex and expensive systems. In addition, most currently available 3D imaging systems also deliver high subject doses, and often limit access to the subject due to use of a gantry, a large area detector or a combination of area detectors.